Science Advisory Report  2013/018

2012 Assessment of 4VWX Silver Hake

Summary

• Landings of 4VWX silver hake in the fishing years ending in 2010 and 2011 were 8,396 and 9,231 mt, respectively, relative to a quota of 15,000 mt.  Landings are constrained by market conditions; there is no indication that a catch lower than the quota is related to reduced abundance.
• The current silver hake fishery catches primarily fish aged 1-2. 
• Total survey biomass has increased to levels comparable to the late 1980s. Age 2+ (a proxy for spawning stock biomass) and 2+ female biomass have also increased.
• The 2009 year class is the largest in the time series.  The incoming 2010 and 2011 year classes are both above average.
• Condition has been generally below the long term average since the early 1990s and is currently near the lowest level in the time series.
• The 2011 (123,000 mt) and 2012 (120,000 mt) model estimates of population biomass were the highest for the 1993-2012 time series.
• The current median estimates of stochastic Maximum Sustainable Yield (MSY), Biomass at MSY (BMSY), and Fishing Mortality at MSY (FMSY) for 4VWX silver hake are 16,000 mt, 59,000 mt, and 0.32, respectively.
• 80% BMSY is proposed as the Upper Stock Reference (USR=47,200 mt) and 40% BMSY is proposed as the Lower Reference Point (LRP=23,600 mt) for 4VWX silver hake.  FMSY is proposed as the limit Removal Reference (RR=0.32). 
• Biomass is expected to be lower in June 2013 and March 2014 than in 2012 regardless of the landings in the 2012/2013 fishing year.   
• Across all landings scenarios examined in the projections (Total Allowable Catch = 0- 18,000 mt), the probability of biomass falling below 80% BMSY in July 2013 was less than 0.1. With landings at FMSY (45,100 mt), the probability of falling below 80% BMSY increases to 0.13. The probability of projected March 2014 biomass falling below these reference levels was less than 0.15. With landings at FMSY, the probability of falling below 80%BMSY increased to 0.32.
• Projections from an aggregate population model, such as that used here, assume mean recruitment and growth across the projected years. The ability of the model to describe future biomass more than one year ahead is uncertain given that silver hake have highly variable recruitment patterns and the fishery prosecutes recruiting individuals (ages 1-2).
• The restrictions on geographic extent of the fishery may preclude exploitation as high as FMSY, since this may represent a higher proportion of the stock biomass than is present in Emerald and LaHave basins and available to be caught.
• Based on observer records, bycatch constitutes less than 4% of the total observed catch.
• The fishery occurs primarily on soft-bottom habitat in Emerald and LaHave basins.  A part of a globally unique population of the large-structure forming sponge, Vazella pourtalesi, is also found in this area and is known to be vulnerable to bottom-tending fishing gear. 

This Science Advisory report is from the December 11, 2012, Review of the Framework and Assessment for 4VWX Silver Hake: Part 3 - Assessment. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.  

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